Active medium for a liquid laser and method of preparation thereof

ABSTRACT

An active medium for a liquid laser containing selenium oxychloride solvated neodymium ions in a solution of phosphorous oxychloride and a Lewis acid. The liquid active medium is prepared by first dissolving a neodymium compound in a mixture of selenium oxychloride and a Lewis acid and then evaporating the solution to form a solid. The resulting solid material is then added to a mixture of phosphorous oxychloride and a Lewis acid.

United States Patent [72] Inventor Kenneth W. French [54] ACTIVE MEDIUM FOR A LIQUID LASER AND METHOD OF PREPARATION THEREOF 9 Claims, 3 Drawing Figs.

[52] U.S. Cl 252/301.4, 331/945, 330/43 [51 Int. Cl C09k 1/08, C09k 1/16, HOls 3/00 [50] Field of Search 252/301.4; 331/945 [56] References Cited UNITED STATES PATENTS 3,404,351 10/1968 Heller 252/3014 OTHER REFERENCES Heller, A High Gain Room-Temperature Liquid Laser:

Trivalent Neodymium in Selenium Oxychloride- Applied Physics Letters, Vol. 9, No. 3, 1st Aug. 1966, pp. 106- 108 Copy in Patent Office Search Center Lempicki et al., Characteristics of ND': SeOCl: Liquid Laser- Applied Physics Letters, Vol. 9, No. 3; 1st Aug. 1966, pp. 108- 1 10 Copy in Patent Office Search Center Blumenthal et al., New Room Temperature Liquid Laser; Nd(III) in POCL;;SnCL .10urna1 of Chemical Physics, Vol.48, No. 12,15 June 1968, pg. 5726 Primary E.\'aminerTobias E. Levow Assistant Examiner-R. D. Edmonds Attorney-Irving Kriegsman ABSTRACT: An active medium for a liquid laser containing selenium oxychloride solvated neodymium ions in a solution of phosphorous oxychloride and a Lewis acid. The liquid active medium is prepared by first dissolving a neodymium compound in a mixture of selenium oxychloride and a Lewis acid and then evaporating the solution to form a solid. The resulting solid material is then added to a mixture of phosphorous oxychloride and a Lewis acid.

ABSORPTION EMISSION INTENSITY (arbitrary unHS) PATENTEUNUVBOIQH 3.623.995

SHEET 1 OF 2 WAVELENGTH (K) Fig. i.

O BS OO BB OO I 9000 A I IOf IOO I l0,00 I |0,80O

WAVELENGTH (3) Fig.

INVENTOR. KENNETH W. FRENCH By R. M/

A770 NEY 1 2 ACTIVE MEDIUM FOR A LIQUID LASER AND METHOD When the first solution containing the active ions in the mix- OF PREPARATION THEREOF ture of selenium oxychloride and a Lewis acid is prepared, the

solution is heated to rovide eva oration d in and thereb BACKGROUND OF THE INVENTION fonn a residual solid. The solid co iitains sele ri iusi oxychloridt This invention [dates to an active medium f a quid laser 5 solvated active ions. These solvated ions are found to dissolve and to a method f preparation h f in a mixture of phosphorous oxychloride and a Lewis acid and The recent development f a high gain room temperature provide a laser medium which exhibits a low threshold and liquid laser utilizing an active medium containing neodymium high output f the dlelech'ic constant of Phosphorous in a solution f Selenium oxychloride and a Lewis acid has ychloride is relatively low, about 14, theaddltton of substandemonstrated that inorganic liquid lasers compare favorably amounts of acme agents to the solution has been hereto in threshold and output with the best known solid-state laser fore ch'flmc'terized by the formation ofa precipitate containing materials, such as neodymium-doped crystals or ruby. The the helm? er, the present method of pre aring 3 characteristics of this type of liquid laser are described in phQsPhorous ofychlonde acme 'P Provldesa l detail in two articles appearing in Applied Physics Letters Vol. 1 5 toxlcny noncorroswe medlum havfng operatmg 9 Na 3 pp 106410 Aug. 1, 1966 characteristics wh ch compare favorably with those of Generally, the inorganic liquid laser exhibits a high quan- Presently ava'lablehqmd acme medla' tum yield of fluorescence and a low power threshold due to Further features advanmges of the nvenilon the reduction of radiationless relaxations of the active agent in Wm F Q more f f from the followmg detalled solution. The radiationless relaxations result in part from the descnpuon ofspeclfic embodlmems meteor high-energy vibrations of bonds involving light atoms, particu- BRIEF DESCRIPTION OF THE DRAWINGS larly hydrogen. Consequently, the achieving of low threshold and high output in a liquid active medium requires that the FIG- 1 shows the absorp ion spectrum of the present active solvent employed contain only heavy atoms. This requirement medium. has limited the number of solvents heretofore suitable for use FIG. 2 shows he emission spectrum of the present active in liquid laser. medium.

In addition, the selection of the solvent used is determined IG 3 is a schematic representation of a liquid laser.

by the solubility of the compound containing the active agent,

typically neodymium ions, in the solvent. This is due primarily DESCRIPTION OF THE PREFERRED EMBODIMENTS to the fact the Power threshold -i the P density hecessa' The present active medium for a liquid laser contains seleniry to produce stimulated emission of radiation, is a function of um l id l d active i i a mixture f the concentration of active ions. In order to obtain the conphosphorous hl id d a Lewi a id, centrations needed for moderate threshold levels, the solvent Th l i o hl ride olvated active ions are prepared employed is characterized a relatively dielectric condissolving a cQmpQund containing the active ion in a mix- Slant s that the f r s between the cation and anion 0f the ture of selenium oxychloride and a Lewis acid. in solution, the compound are reduced thereby lessening the tendency of the compound dissociates into cations and anions with the active compound to precipitate. The dielectric constant of the 501- i i ll a rare earth i constituting h Cation Th Vent selenium oxychloride is approximately 'i it tion forms a complex with the solvent so that the cation is solhas been necessary to add an acidifying agent to h Selenium 40 vated by a surrounding zone of oriented solvent ions. The oxychloride solution in order to provide low threshold operao le for-med by the solvated cation is determined by the li n- Th ag nt add d s a L is a i d n as 8 Substance number of immediate neighbors the cation favors. in the case which can accept an electron pair from a bas A m r of the neodymium cation, the complex contains 8, 9, or 10 imde ail description f 3 lo hr sh l iquid aCtlVe medium mediate neighbors. The immediate neighbor atom, in this case utilizing a Lewis acid to increase the active ion concentration oxygen, forms a coordinate bond with the cation. The imi n in i h copen ing P appli ati N mediate neighbor shares a pair of electrons with the cation. 604,362, filed Dec. 23, I966 and assigned to the same as- The selenium oxychloride is characterized by a relatively signeei high dielectric constant. However, a Lewis acid is required to The selenium oxychloride based liquid medium has n be added to the selenium oxychloride in order to increase the found to combine high l and low threshold and demohconcentration of the active agent in the solvent. A Lewis acid strates that liquid media compare favorably with solid media. is defined as a substance which can accept an electron pair However, laser solutions prepared with this solvent are highly f a base, When added to the selenium oxychloride, the corrosive and toxic. Consequently, these solutions are difficult L wi acid combines with the anion of the solvent, ty ically a to handle and contain. Since one of the important features of a hloride ion. The acid enhances the solubility of the comliquid medium is its ability to be circulated, the combination pound i th solvent b bi i i h d i ff removof toxicity and corrosiveness has increased the complexity of ing chloride anions from the solution. This provides additional the system. As a result, the development of low toxicity and solvent cations in accordance with the solubility product of substantially noncorrosive liquid media having performance the solvent and, therefore, increases the number of active ions characteristics which are comparable to those of the selenium in the solution.

The compound containing the active ion is typically a chloride or oxide. In addition, the active ion is normally a rare SUMMARY OF THE INVENTION earth ion and preferably neodymium since it has an absorbance characteristic which enables it to be readily pumped by commercially available flashlamps. The amount of the Lewis acid utilized in the preparation of the solution containing the selenium oxychloride solvent is, in practice, determined primarily by the amount of the compound added to the solution. The following examples show the preparation of the 70 selenium oxychloride solution for different compounds and Lewis acids.

oxychloride medium is desirable.

This invention relates to an active medium for a liquid laser and a method of preparation thereof. in particular, the active medium provided by the present invention exhibits a low toxicity and the low corrosiveness desired in circulating liquid laser systems.

The active medium utilizes selenium oxychloride solvated active ions which are added to a mixture of phosphorous oxychloride and a Lewis acid. The solvated active ions, typically neodymium, are prepared from a first solution containing EXAMPLE] acidified selenium oxychloride as the solvent. The selenium oxychloride solvent is acidified by the addition of a Lewis acid One hundred grams of the anhydrous Lewis acid SnCl, was

to promote the solubility of the active ions therein. 7 diluted to 0.2 liter by the gradual addition of vacuum distilled EXAMPLE II Seventy-five grams of anhydrous Lewis acid SbCl, were diluted to 0.1 liter by the gradual addition of vacuum distilled SeOCI Then 75 grams of anhydrous neodymium trichloride, NdCl was added to the mixture. The solution was then slowly brought to a boil at about 120 C. at a pressure of 40 mm. of Hg.

While the above examples recite SnCl. and SbCl as the Lewis acids, other Lewis acids such as SnBr GeCl TiCl, and 80;, may be employed. The concentration of the active ions in the solution is not critical since the prepared selenium oxychloride solution is evaporation dried by the boiling.

The boiling of the solution results in the formation of a wet solid which begins to appear in substantial quantities when approximately 60 percent of the liquid has been removed. The actual period of boiling depends upon the initial viscosity of the selenium oxychloride solution and the degree of dryness desired in the resulting solid. After boiling for a period of about 30 minutes, approximately 60 to 70 percent of the liquid is removed and solid matter is observed. The remaining solution was then cooled to room temperature in a period of about 15 minutes whereupon the remainder of the liquid entered a solid phase. The result is a wet solid containing selenium oxychloride solvated ions. While the above-described relatively short boiling period provides a wet solid, the period may be extended to produce a dry solid without affecting the operating characteristics of the active medium provided by this method.

As mentioned, the solid contains solvated active ions. This solid is found to be readily dissolved in a mixture of phosphorous oxychloride and a Lewis acid. The low dielectric constant of phosphorous oxychloride has heretofore limited the concentration of active ions that can be dissolved in the solution even with the addition of the Lewis acid acidifying agent. However, the concentrations, typically 0.3M, obtained by the addition of selenium oxychloride solvated ions provide a liquid active medium having a low threshold and a high output. In addition, the present medium is characterized by a low toxicity and a noncorrosiveness unlike media utilizing selenium oxychloride as the solvent.

The solid, which in the case of neodymium is a blue-purple color, is added to a mixture of phosphorous oxychloride and a Lewis acid. The mixture is typically a 5 to 1 volume mixture of phosphorous oxychloride and the Lewis acid. The same Lewis acid can be used as in the preparation of the first solution. However, different Lewis acids may be employed if desired.

The amount of Lewis acid is determined primarily by the amount of solvated ion added to the mixture. In practice, the amount of solvated ion added to the mixture of phosphorous oxychloride and Lewis acid is that required to obtain an active ion concentration within the range of 0. IM to 1.0M. The corresponding amounts of Lewis acid ranged from 0. IM to 2.0M.

The spectral distribution of absorbance and emission for the selenium oxychloride solvated neodymium ions in a mixture of phosphorous oxychloride and Lewis acid are shown in F IGS. l and 2. These spectrai distributions are found to be essentially independent of the particular compound and Lewis acid employed. The present medium was tested and operated in the laser structure shown in FIG. 3. The laser structure is shown comprising a hollow transparent cylinder 11 which may be made of any material which transmits light in the pumping region, such as quartz, pyrex, and the like. In practice, the

cylinder 11 may be formed of commercial glass tubing. First and second optically flat end seals 12 and 13 are fused to the ends of the cylinder. These end-seals may be either transparent to the radiation emitted by the laser or provided with reflecting coatings depending on the desired application. TyR- ical cylinders have bore diameters of 2 to 10 mm. and lengt s ranging between 2 and 12 inches.

The end-sealed cylinder is filled with the active liquid medium through side-arm 19 which is then sealed. If the medium is to be circulated a second side-arm may be provided and the side-arms used as input and output ports. A flashlamp 14 is placed around the cylinder. Electrodes l5 and 16 are connected to the ends of the helical flashtube. A capacitor 17 is coupled between the electrodes. Power supply 18 maintains a constant voltage of about 10 kilovolts across capacitor 17. The structure is maintained at room temperature.

When the lamp is flashed by applying a 20 kilovolt trigger pulse to wire 24 from trigger source 23, energy is absorbed by the active medium 20 and the stimulated emission is obtained through the end-seals l2 and 13. The wavelength of the stimulated emission is primarily detennined by the active ion in the liquid medium.

The low threshold high energy output and sharpness of the emission line obtained with a laser utilizing the present medium compares favorably with the known selenium oxychloride media. The peak fluorescent emittance from the present liquid medium is a measure of the gain of the laser and is essentially equal to the emittance of a neodymium ion in selenium oxychloride medium under identical excitation.

While many modifications and variations may be made in the aforedescribed invention, it will be recognized that many modifications and variations may be made therein without departing from the spirit and scope of the invention.

What is claimed is:

1. A method of making a liquid active medium for a laser which comprises the steps of a, heating a first solution containing selenium oxychloride, a

Lewis acid and a compound containing an active ion to evaporate a portion of said solution and form a solid, said solid containing selenium oxychloride solvated active ions, and

b. adding the solid to a mixture of phosphorous oxychloride and a Lewis acid to form a second solution, said second solution constituting an active medium for a liquid laser.

2. The method of claim 1 wherein said first solution is heated to evaporate approximately 60 percent of the liquid.

3. The method of claim 2 further comprising the step of cooling said first solution to solidify the remaining liquid.

4. The method of claim 1 wherein said first solution contains a rare earth compound.

5. The method of claim 4 wherein said rare compound is selected from the group consisting of chlorides and oxides.

6. The method of claim 4 wherein said rare earth compound is a compound containing neodymium.

7. The method of claim 6 wherein said first and second solutions contain a Lewis acid selected from the group consisting of SnC1.,, SbCl SnDn, GeC1.,,TiC1., and S0 8. An active medium for a liquid laser which consists essentially of a solution containing a. selenium oxychloride solvated active neodymium ions;

b. phosphorous oxychloride, and

c. a Lewis acid, said acid enhancing the solubility of said solvated ions in phosphorous oxychloride.

9. The medium of claim 8 wherein said Lewis acid is selected from the group consisting of SnC1.,, SbC1 SnBr GeCl.,, TiCl,, and

k a: t t 

2. The method of claim 1 wherein said first solution is heated to evaporate approximately 60 percent of the liquid.
 3. The method of claim 2 further comprising the step of cooling said first solution to solidify the remaining liquid.
 4. The method of claim 1 wherein said first solution contains a rare earth compound.
 5. The method of claim 4 wherein said rare compound is selected from the group consisting of chlorides and oxides.
 6. The method of claim 4 wherein said rare earth compound is a compound containing neodymium.
 7. The method of claim 6 wherein said first and second solutions contain a Lewis acid selected from the group consisting of SnCl4, SbCl5, SnDr4, GeCl4, TiCl4 and SO3.
 8. An active medium for a liquid laser which consists essentially of a solution containing a. selenium oxychloride solvated active neodymium ions; b. phosphorous oxychloride, and c. a Lewis acid, said acid enhancing the solubility of said solvated ions in phosphorous oxychloride.
 9. The medium of claim 8 wherein said Lewis acid is selected from the group consisting of SnCl4, SbCl5, SnBr4, GeCl4, TiCl4, and SO3. 